1. Field of the Invention
This invention relates to a plasma display panel, and more particularly to an energy recovering apparatus and method and a method of driving a plasma display panel using the same that are adaptive for improving light-emission efficiency.
2. Description of the Related Art
Generally, a plasma display panel (PDP) radiates a phosphorous material using an ultraviolet ray with a wavelength of 147 nm generated upon discharge of an inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe, to thereby display a picture including characters and graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development. Particularly, since a three-electrode, alternating current (AC) surface-discharge PDP has wall charges accumulated in the surface thereof upon discharge and protects electrodes from a sputtering generated by the discharge, it has advantages of a low-voltage driving and a long life.
FIG. 1 is a perspective view showing a discharge cell structure of a conventional plasma display panel.
Referring to FIG. 1, a discharge cell of the conventional three-electrode, AC surface-discharge PDP includes a scan electrode Y and a sustain electrode Z provided on an upper substrate 10, and an address electrode X provided on a lower substrate 18. The scan electrode Y and the sustain electrode Z include transparent electrodes 12Y and 12Z, and metal bus electrodes 13Y and 13Z having a smaller line width than the transparent electrodes 12Y and 12Z and provided at one edge of the transparent electrodes 12Y and 12Z, respectively.
The transparent electrodes 12Y and 12Z are usually formed from indium-tin-oxide (ITO) on the upper substrate 10. The metal bus electrodes 13Y and 13Z are usually formed from a metal such as chrome (Cr) on the transparent electrodes 12Y and 12Z to thereby reduce a voltage drop caused by the transparent electrodes 12Y and 12Z having a high resistance. On the upper substrate 10 provided with the scan electrode Y and the sustain electrode Z in parallel, an upper dielectric layer 14 and a protective film 16 are disposed. Wall charges generated upon plasma discharge are accumulated into the upper dielectric layer 14. The protective film 16 prevents a damage of the upper dielectric layer 14 caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film 16 is usually made from magnesium oxide (MgO).
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 provided with the address electrode X. The surfaces of the lower dielectric layer 22 and the barrier ribs 24 are coated with a phosphorous material layer 26. The address electrode X is formed in a direction crossing the scan electrode Y and the sustain electrode Z. The barrier rib 24 is formed in a stripe or lattice shape to thereby prevent an ultraviolet ray and a visible light generated by a discharge from being leaked to the adjacent cells. The phosphorous material layer 26 is excited by an ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. An inactive mixture gas is injected into a discharge space defined between the upper/lower substrates 10 and 18 and the barrier rib 24.
Such a PDP is driven with being separated into a plurality of sub-fields. In each sub-field interval, a light-emission having a frequency proportional to a weighting value of video data is progressed to thereby make a gray level display. Each of the sub-fields is driven with being again divided into a reset period, an address period and a sustain period.
Herein, the reset period is a time interval for forming uniform wall charges on the discharge cell; the address period is a time interval for generating a selective address discharge depending upon a logical value of video data; and the sustain period is a time interval for sustaining a discharge from a discharge cell at which the address discharge has been generated.
The sustain discharge of the AC surface-discharge PDP driven as mentioned above requires a high voltage more than hundreds of volts. Accordingly, an energy recovering apparatus is used for the purpose of minimizing a driving power required for the sustain discharge. The energy recovering apparatus recovers a voltage between the scan electrode Y and the sustain electrode Z to uses the recovered voltage as a driving voltage upon the next discharge. 
FIG. 2 shows an energy recovering apparatus provided at the scan electrode Y in order to recover a sustain discharge voltage. In real, the energy recovering apparatus also is symmetrically provided at the sustain electrode Z around a panel capacitor Cp.
Referring to FIG. 2, the conventional energy recovering apparatus includes an inductor L connected between a panel capacitor Cp and a source capacitor Cs, first and third switches S1 and S3 connected, in parallel, between the source capacitor Cs and the inductor L, diodes D5 and D6 connected between the first and third switches S1 and S3 and the inductor L, and second and fourth switches S2 and S4 connected, in parallel, between the panel capacitor Cp and the inductor L.
The panel capacitor Cp is to equivalently express a capacitance formed between the scan electrode Y and the sustain electrode Z. The second switch S2 is connected to a reference voltage source Vs while the fourth switch S4 is connected to a ground voltage source GND. The source capacitor Cs recovers and charges a voltage charged in the panel capacitor Cp upon sustain discharge and re-supply the charged voltage to the panel capacitor Cp.
To this end, the source capacitor Cs has a capacitance value capable of charging a voltage of Vs/2 corresponding to a half value of the reference voltage source Vs. The inductor L forms a resonance circuit along with the panel capacitor Cp. The first to fourth switches S1 to S4 control a current flow. The fifth and sixth diodes D5 and D6 prevent a current from flowing in a backward direction. Internal diodes D1 to D4 provided at the first to fourth switches S1 to S4, respectively also prevent a flow of backward current.
FIG. 3 is a timing diagram and a waveform diagram representing an on/off timing of the switches shown in FIG. 2 and an output waveform of the panel capacitor.
An operation procedure of the energy recovering apparatus will be described assuming that 0 volt has been charged in the panel capacitor Cp and a Vs/2 voltage has been charged in the source capacitor Cs prior to a T1 interval.
In a T1 interval, the first switch S1 is turned on, to thereby form a current path extending from the source capacitor Cs, via the first switch S1, the inductor L, into the panel capacitor Cp. If the current path is formed, then a Vs/2 voltage charged in the source capacitor Cs is applied to the panel capacitor Cp. At this time, a Vs voltage equal to twice the voltage of the source capacitor Cs is charged in the panel capacitor Cp because the inductor L and the panel capacitor Cp form a serial resonance circuit.
In a T2 interval, the second switch S2 is turned on. If the second switch S2 is turned on, then a voltage of the reference voltage source Vs is applied to the panel capacitor Cp. In other words, if the second switch S2 is turned on, then a voltage value of the reference voltage source Vs is applied to the panel capacitor Cp, thereby preventing the voltage value of the panel capacitor Cp from being dropped into less than a voltage of the reference voltage source Vs and thus making a stable generation of the sustain discharge. Herein, since a voltage of the panel capacitor Cp has risen until Vs in the T1 interval, a voltage value supplied from the exterior during the T2 interval can be minimized. In other words, power consumption can be reduced.
In a T3 interval, the first switch S1 is turned off. At this time, the panel capacitor Cp keeps a voltage of the reference voltage source Vs. In a T4 interval, the second switch S2 is turned off while the third switch S3 is turned on. If the third switch S3 is turned on, then a current path extending from the panel capacitor Cp, via the inductor L and the third switch S3, into the source capacitor Cs is formed to recover a voltage Vcp charged in the panel capacitor Cp into the source capacitor Cs. At this time, a Vs/2 voltage is charged in the source capacitor Cs.
In a T5 interval, the fourth switch S4 is turned on. If the fourth switch S4 is turned on, then a current path between the panel capacitor Cp and the ground voltage source GND is formed, thereby allowing a voltage of the panel capacitor Cp to drop into 0 volt. In a T6 interval, the third switch S3 is turned off. In real, an alternating current driving pulse supplied to the scan electrode Y and the sustain electrode Z has the T1 to T6 intervals repeated periodically.
More specifically, a rectangular waveform, as shown in FIG. 4, having a predetermined rising slope and a predetermined falling slope is alternately applied to the scan electrode Y and the sustain electrode Z during the sustain period to thereby cause a sustain discharge. However, an application of the rectangular waveform during the sustain period raises a problem of a low light-emission efficiency. In other words, if a sustain pulse having a rectangular waveform as shown in FIG. 4 is applied, then only once discharge is generated for a short time at an initial period of the sustaining pulse (or the rectangular waveform). Herein, since an amount of a generated light is in proportion to a discharge time (or period), the conventional PDP has a low light-emission efficiency.
In order to overcome such a problem, a method of applying a ramp pulse as a sustaining pulse as shown in FIG. 5 is disclosed in Korea Patent Laid-open Gazette No. 2001-000955.
Referring to FIG. 5, a sustaining pulse generated from another conventional energy recovering apparatus suddenly rises until approximately a voltage of the reference voltage source Vs and then slowly rises from the reference voltage Vs until a peak voltage Vr at a predetermined slope. Thereafter, the sustaining pulse suddenly falls from the peak voltage Vr into a voltage of the ground voltage source GND. Herein, a discharge is generated when the sustaining pulse rises from the reference voltage Vs into the peak voltage Vr at a predetermined slope after rising until approximately a voltage of the reference voltage source Vs and when the sustaining pulse falls from the peak voltage Vr into a voltage of the ground voltage source GND. In other words, the sustaining pulse generated from the energy recovering apparatus causes approximately three times discharge to thereby improve light-emission efficiency.
However, the energy recovering apparatus as shown in FIG. 5 has a drawback in that, since it uses a ramp pulse, power consumption is wasted. More specifically, a ramp pulse rising slowly at a predetermined slope is generated by utilizing a resistor R. Accordingly, another conventional embodiment raises a problem in that an additional power consumption is wasted due to the resistor R.
Furthermore, the energy recovering apparatus shown in FIG. 5 generates a self-erasing discharge when the sustaining pulse falls from the peak voltage Vr into a voltage of the ground voltage source GND. If the self-erasing discharge is generated, then wall charges formed at the discharge cell are erased. In this case, as the wall charges formed at the discharge cell are erased, a sustain discharge is not generated when the next sustaining pulse is applied. In other words, when a wall voltage of the wall charges formed at the discharge cell is added to a voltage of the sustaining pulse to thereby cause a voltage difference more than a firing voltage between two electrodes, a stable sustain discharge can be generated. Thus, if wall charges formed at the discharge cell are erased, then a voltage difference between two electrodes becomes lower than the firing voltage, so that a sustain discharge is not generated.